Weighing systems for producing a product charge of precise weight are well known in the art and include systems that employ one of several combinatorial weighing techniques. In general, these mechanisms obtain a precise weight product charge by combining the contents of a plurality of buckets or hoppers, each of which contains a portion of the product charge. A controller reads the weight of each hopper, searches for the hopper weight combination which most closely approximates the desired weight, and subsequently dumps the contents of the corresponding hoppers.
Known combination weighing devices include the weighing apparatus disclosed in U.S. Pat. No. 4,515,231. That apparatus is characterized by a serial weighing operation in which articles are first provided to a plurality of fill-to-weight cutoff pool hoppers. After the weight of the product charges in the pool hoppers has been determined, the contents thereof are fed to corresponding weighing hoppers. The weighing of each of the weighing hoppers is then measured and a computer determines that combination of hoppers whose weight sum is equal or closest to a desired product charge weight. The U.S. Pat. No. 4,515,231 apparatus is most useful in handling light products or products apt to cling together in bunches. However, that apparatus is burdened by two discrete weighing operations. Moreover, the speed of operation of the combinatorial weights is necessarily limited by the filling speed of the fill-to-weight cutoff pool hoppers.
U.S. Pat. No. 4,418,771 discloses a combination weighing method and apparatus wherein quantities of the product of targeted weight are distributed to a plurality of scale controlled hoppers for accurate weighing. The weighed product charge is fed from each of the scale controlled hoppers to a plurality of storage cups associated with each of the hoppers and the product weight associated with each storage cup is registered. Specific combinations of storage cups are tested to determine whether the combined product weights add to make the desired weight within acceptable limits. The method and apparatus is characterized by a controller which will examine only a subset of hoppers rather than all of them to find a combination which will provide the desired weight product charge. If no combination produces a total product charge within selected weight limits, the controller will broaden the limits and repeat the cycle.
Known combinatorial weighing systems which will generate a product charge from two or more different articles include the weighing system disclosed in U.S. Pat. No. 4,473,126. Disclosed therein is a weighing system which includes a separate conventional combination weigher for each of the different articles which comprise the product charge. U.S. Pat. No. 4,549,617 teaches a combinatorial weighing system having a method of setting a target value (weight or number) for each of the component articles and supplying a plurality of combinatorial weighing machines. For each category of articles and from all combinations of the weighing machines, a controller determines the best combination therefrom whose total value (weight or number) is equal to the target value set for that category.
The combinatorial weighing method disclosed in U.S. Pat. No. 4,522,274 obtains a product charge having a mixture of articles of different categories wherein the articles in each category are contained in the mixture at a number ratio approximately equal to a target number. The method includes the steps of setting a number for each category to provide a number ratio closest to a target category number ratio, and measuring the total weight of a primary mixture obtained by extracting the set number of articles in each category and mixing these articles. If the weight of the primary mixture is initially outside of a minimum, a controller computes the weight difference between the primary mixture and target weight and provides supplemental articles to make up the short fall. The method provides for uniformity in the product weight to target number ratio as opposed to component distribution.
The combination weighing device taught in U.S. Pat. No. 4,388,975, simultaneously weighs a plurality of articles in weighing balances and a controller which selects a plurality of the weighing balances to comprise a total weight of articles within a predetermined range. The device is characterized by a controller which causes one or more of the specified weighing balances to always enter into the selected combination to insure that each package contains articles from selected weighing balances.
In the commonly owned U.S. Pat. No. 4,678,046, there is disclosed a combination weighing apparatus for two combined products which is characterized by one or more combinatorial weighing apparatus that separately provide the product constituents of a blended product charge. The apparatus disclosed therein is particularly useful in those instances where the product ratios are approximately even, such as multicomponent dog foods, where each product constituent comprises generally between 40 and 60% of the total weight. Existing combinatorial weighers for producing blended product charges are most cost effective in those applications where the product component weight ratios are approximately equal. However, with many blended products the minor constituent comprises only a small fraction (approximately 10%) of the product charge weight. Weighing systems which employ a combinatorial weigher for each major and minor product constituent under-utilize the minor constituent weigher and are, therefore, unnecessarily expensive.
For those situations where product preblending is not possible, it would be advantageous to have a combinatorial weigher for preparing a blended or multi-component product charge which is inexpensive and simple to construct, which is cost effective, which can be adapted to existing combination weighers and which avoids a separate combination weigher for each product. The present invention is drawn to such a weighing system.